Many industrial processes require hot water in the range of 60-90° C. for heating applications, like paint booth in automobile industry, paper industry, food industry, hotels, and the like. Extensive amount of energy is consumed during the heating application, which adds to the operating costs of the process. Generally, the energy sources used for heating water are fossil fuels including natural gas, liquefied petroleum gas, oil, or solid fuels. These fuels may be consumed directly or by the use of electricity, which may be derived from the above mentioned energy sources. Alternatively, hot water can be generated using solar energy, heat pumps, hot water heat recycling or geothermal heating. The hot water thus generated is sent to the application point where it loses the heat and is then recycled to the hot water generating system. These industries also normally require chilled water/refrigeration for the various process applications.
Refrigeration is commonly used in industries to liquefy gases like oxygen, nitrogen, propane and methane; in compressed air purification to condense water vapor from compressed air to reduce its moisture content; in oil refineries, chemical plants and petrochemical plants to maintain a low process temperature; and metallurgy industries to temper steel and cutlery. A heat pump is ideal for industrial applications that require both heating and cooling water, wherein the same mechanical refrigeration system can be used to obtain both the effects. With stringent pollution control regulations, application of heat pumps in industries has become important, since the technology helps to reduce emissions, improves efficiency, and limits the use of ground water for cooling. Also, heat pumps are efficient heating and cooling systems that significantly reduce the energy costs.
The heat pumps commonly used in industrial operations are based on a vapor compression or a vapor absorption cycle. Absorption heat pumps are thermally driven, which means that heat rather than mechanical energy is supplied to drive the cycle. Further, absorption heat pumps for space conditioning are often gas-fired, while industrial installations are usually driven by high-pressure steam or waste heat. The absorption systems utilize the ability of liquids or salts to absorb vapors of a working fluid to obtain the heating and the cooling effect.
The vapor compression cycle uses high grade energy from mechanical inputs while the vapor absorption cycle uses energy input from waste heat or heat derived from solar collectors. Thus, vapor absorption heat pumps substantially reduce the operating costs as they use low-grade waste heat. Also, the vapor absorption systems use non-ozone depleting refrigerants (water) and require much lesser electricity compared to the vapor compression systems. These systems are even more beneficial for industrial applications where waste heat can be used to generate steam/hot water.
The need for energy conservation has been highlighted by concerns about the environment, leading to development of energy efficient heating and cooling systems. Increased attention has been directed towards development of cost-effective and efficient heat pumps, that can provide heating and cooling, thus, reduce the energy consumption. As a result, the vapor absorption systems are gaining favor over conventional vapor compression heat pumps in industrial applications, as they use little energy and are environmental friendly.
The basic vapor absorption cycle employs two fluids, the refrigerant and the absorbent. Most commonly, lithium bromide (Li—Br)-water are used as the absorbent-refrigerant pair. In the absorption cycle the low-pressure refrigerant vapor is absorbed into the absorbent releasing a large amount of heat. The liquid refrigerant/absorbent solution is pumped to a high-operating pressure generator, where heat is provided from a gas burner, steam, hot water or hot gases. The heat causes the refrigerant to desorb from the absorbent and vaporize. These vapors flow to a condenser, where the heat is rejected and the refrigerant is condensed to a high-pressure liquid. This liquid refrigerant is then sent to a low-pressure evaporator, where it evaporates by absorbing heat and providing the cooling effect. The concentrated absorbent in the generator is then sent to the absorber, where it is recombined with the low-pressure refrigerant vapors returning from the evaporator, repeating the cycle. The vapor absorption machines can be used for heating applications by passing the hot refrigerant (water) vapors directly from the high temperature generator to the evaporator. These systems utilize heat source such as steam, hot water or hot gases leaving a boiler, turbine or engine generators.
Commercially, absorption heat pumps can be single-effect or multi-effect. The process discussed above discloses the working of a single-effect vapor absorption system. In single-effect absorption systems, the heat released during the chemical process of absorbing refrigerant vapor into the absorbent rich-stream, is rejected to the environment. In a multi-effect absorption system, some of this energy is utilized as the driving force to generate more refrigerant vapors. The more vapor generated per unit of heat input, greater the cooling capacity and higher the overall operating efficiency. A double-effect absorption system uses two generators including a high temperature and a low temperature generator, paired with a single condenser, absorber, and evaporator.
The conventional vapor absorption systems can only generate hot water up to 40-43° C., thus, limiting the applications of these systems in industries. Also, these systems can only be used for heating applications by passing the hot refrigerant (water) vapors directly from the high temperature generator to the evaporator. During this operation the vapor absorption system can only function as hot water generator and simultaneous refrigeration effect cannot be obtained. In conventional type of heating-cooling systems, switching between cooling operations and heating operations can be complicated and additional components like generators, pumps and chillers may be required. This adds to the initial capital investment and the operation and maintenance costs in terms of heat and electrical inputs and utilities. Therefore, a suitable system is required that will simultaneously provide heating and refrigeration effect without any additional components and costs.
Several efforts have been made for providing a vapor absorption heat pump which provides simultaneous heating and cooling effect, some of these works are listed in the prior art cited below:
U.S. Pat. No. 6,405,551B1 discloses a heating apparatus provided with a refrigeration cycle which can be used for heating, cooling and supplying hot water. The apparatus as disclosed in U.S. Pat. No. 6,405,551 comprises a compressor, a condenser, an evaporator and a first and a second heat exchanger. The first heat exchanger is always used as a heating medium for feed water or bath water while the second heat exchanger is used to provide either heating or cooling by selectively operating the heat exchanger as a condenser or an evaporator, by adequately switching the refrigeration ducts. The apparatus as disclosed in U.S. Pat. No. 6,405,551, is primarily used to provide hot water having temperature up to 60° C. and suitable for household applications.
WO2009/063494A2 discloses a Li—Br vapor absorption machine for providing refrigeration effect. The machine as disclosed in WO2009/063494 comprises of a high temperature generator connected to a furnace to receive a direct heat input by combustion of solid fuels. The machine as disclosed in WO2009/063494 is only used to provide a refrigeration effect. Large quantity of energy consumption and higher CO2 emissions, are some of the drawbacks of the machine as disclosed in WO2009/063494.
Therefore, there is felt a need for a system that will simultaneously provide the heating and the cooling effect, utilize less energy, reduce CO2 emissions, reduce the operating costs and is suitable for various applications.